Rotating surface based antennas can be parabolic, flat plate arrays or pleased arrays (or any other arbitrary shaped antennas) which can be steered electronically in elevation. The latter two types of antennas are characterized by an array of radiating elements and an elaborate network of power distribution components. It is very difficult to diagnose these antennas, especially in field conditions, and after years of operational use. Ordinarily, modern systems include automatic on-line testing that tests most of the prime components but does not usually test the radiating elements. Any known radiating element testing which may be provided is either quite crude and does not provide accurate and high resolution fault detection and isolation, or it is very difficult to perform, especially in field conditions.
Known prior techniques for providing field diagnosis of the radiating elements of the antenna include near field probing and far field pattern measurement. Near field probing requires that the antenna be stopped from rotating and that a probe sample the near field across the whole aperture. This techniques requires the construction of scaffolds and precise probe guide fixtures around the antenna. As a result, operational use of the antenna is stopped for a period which may last for several days. Other known near field techniques require that the test probe be moved in a circular path near the array, requiring a complex and highly accurate mechanical apparatus. Such near field testers are expensive.
Far field tests include placement of a radiating element in the far field and performing radiation pattern measurements. These techniques are elaborate logistically, as they require another site with line of sight to the antenna, and higher power for the test signal due to the greater distance. In addition, multi-path signals are also usually present which contaminate the test results.